The peak performance of an electric machine can be enhanced by effective cooling of windings of the stator. Heat is generated predominantly in the windings of the stator. Eddy currents in the rotor are high, but contribute very little to thermal losses, thus reducing the need for forced cooling. Often a liquid coolant is employed to extract heat from the stator. In conventional electric motors, the coolant may contact the rotor with little consequence. However, in very high speed motors, such as an electric motor coupled to a turbomachine, in which the speeds can approach 350,000 rpm, it is desirable to avoid oil contacting the rotor to avoid high losses due to a high shear rate of the coolant. A system and method to provide liquid coolant onto the windings of the stator, while avoiding coolant contact with the rotor, is sought.
In systems in which the coolant is a lubricant that is also provided to bearings associated with the electric motor or turbomachine, lubrication of the bearings should be maintained at all times during operation to maintain the system's integrity.
If the turbomachine associated with the electric motor operates at high temperature, another contributor to high temperatures in the electric machine is due to heat transfer, primarily radiation, from hot components of the turbomachine to the electric motor.